The present invention relates to a method of cleaning substrates, particularly a method of cleaning substrates suitable for cleaning glass substrates for liquid crystal devices wherein dirt on a glass substrate causing an inferior product is removed during a liquid crystal device production process.
There have been known wet cleaning techniques using pure water for cleaning substrates for precision devices or appliances, such as glass substrates for liquid crystal devices. In the case of cleaning a glass substrate for a liquid crystal device already provided with a pattern of electrodes and before provision of an alignment film, for example, it has been ordinarily practiced to first remove dirt, such as dust and inorganic matter, by a combination of spraying, high pressure showering and/or ultrasonic cleaning respectively using pure water, optionally with brushing or ultrasonic cleaning with a detergent and cationic pure water as a pretreatment, and drain the water as by an air knife, a spinner or pulling out from warm pure water, or dry the substrate with, e.g., vapor of IPA (isopropyl alcohol).
It is also known to thereafter heat the glass substrate to about 150° C. and irradiate the substrate with ultraviolet rays at wavelengths of 184.9 nm and 253.7 nm so as to have oxygen in air absorb the ultraviolet rays at 184.9 nm to generate ozone and have the ozone absorb the ultraviolet rays at 253.7 nm to generate oxygen radicals, by which organic matter is decomposed and removed.
However, the above-mentioned first washing with pure water for removal of dust or inorganic matter with pure water as by a combination of spraying, high pressure showering, ultrasonic cleaning, etc., requires some length of time, thus leading to an inferior throughput of the cleaning apparatus or requiring an elongated apparatus in order to retain a high throughput using the same length of time. Further, a large amount of water is required per sheet of glass substrate, and the cleaning cost is considerably expensive.
Further, if the pre-cleaning by brushing or ultrasonic cleaning using a detergent is performed before the cleaning with pure water, it is possible to obtain a sufficient cleaning effect even if a shorter time is used for the cleaning with pure water. However, for an identical throughput, this additionally requires a cleaning step using a detergent and a rinsing step, so that the total length of the required cleaning apparatus is not substantially changed. Further, the required amount of pure water is not substantially changed either because the rinsing step after the cleaning with a detergent requires an additional amount of pure water, thus also requiring a high process cost.